With the invention and application of new semiconductor devices, the luminous efficiency and luminous intensity of LED (Light Emitting Diode) are increasingly improved. LEDs are gradually becoming a new generation of light source. Currently, the LEDs are usually driven by constant current. Constant current drive circuits are achieved through dedicated LED driver chips. When adjusting the brightness of an LED, a serial digital signal and PWM (Pulse Width Modulation) signal would be added to the LED constant current driver chip. This dimming control method uses PWM wave to adjust the pulse duty cycle of the power switch transistor in the high frequency inverter to realize the adjustment of the LED output power.
The principle is that, if the power switch transistor is operating in the ZVS (Zero Voltage Switch) state when the power switch transistor is ON, the power switch transistor will achieve a ZCS (Zero Current Switch) operating state by means of an absorption capacitor at the instant of being turned off, so that the ZVS operating state can be achieved while EMI (Electromagnetic Interference) and the electrical stress of the power switch transistor can be significantly reduced. However, if the pulse duty cycle of PWM wave is too small to keep the continuousness of the drive current, the power switch transistor will lose the ZVS operating conditions, resulting in the stroboscopic situation of LED lights. In addition, the generation of PWM waves requires an external waveform generator so as to increase the complexity and cost of the circuit.